[WHEEL AND FIXED CASES.]
Wheel cases may be 55⁄8 inches long. Cut the paper, without waste, into 4 strips, each 29 inches long. Fixed cases may be 71⁄4 inches long: cut the paper the other way of the sheet, into 4 strips, each 221⁄2 inches long. The extra length, for fixed cases, is to allow of their being reported; that is, filled at the end, with an inch, or more, of grain powder, to make a bang like a squib. The cases are to be gauged to the thickness of roman candle cases, but choked like rockets; 5⁄8 internal, and 7⁄8 external, are a good size. Two solid drifts will be required for wheel cases; one 51⁄2 inches long, besides the head; the other 3 inches: for the fixed cases it will be necessary to have one of 71⁄4 inches. They may be turned of box, beech, or ash; but gun-metal drifts are best, though by no means indispensable. If they are cast in gun-metal, they will simply require filing in the rough places. The cases are to be rammed solid throughout, on a foot, fig. 42, turned in one piece, with a nipple, and a pin 1⁄3 of a diameter thick, and just high enough to keep the choke clear.
In all wheel and fixed cases, whatever the remainder of the fuse may be, begin by putting in one scoop of starting fire; this, when malleted firmly in, should fill about 3⁄8 of an inch in the case. The subsequent fuse can be selected from the Tables. The choke may be protected with a little clay, before the starting fire, like rockets, if thought desirable: no clay is to be used anywhere else. Wheel cases containing steel-filings are termed brilliant.
To prime the cases, very slightly damp some meal powder, by sprinkling it with a few drops of water; mix and chop it up, or mince it, as it were, with a knife: put a little into the mouth of the case, press the nipple, fig. 42, into it, and work it round; this will prime the choke and the mouth at once, still leaving the choke clear; or, paint the choke and mouth with the sash-tool, with meal paste, just sufficient to wet them, then plunge them into dry meal, give them a rap to shake off the superfluous dust, and lay them by to dry.
Wheel and fixed cases need not be choked at all, but plugged 1⁄4 of an inch, with plaster of paris, as directed for roman candles. When dry, charge them by setting them flat on the block, without using the foot. Mallet in a scoop of starting fire, then the other. Afterwards, when a number are charged, bore through the centre of the plaster, with a shell-bit, 1⁄3 the diameter of the case; insert a piece of match in the hole; wash the face of the plaster over with meal paste, and plunge into dry meal. A sheet of double-crown makes 8 wheel case envelopes (2.2.2) 10 by 71⁄2, so that the void at each end, to receive the match, is nearly 1 inch.
It is not possible to devise a formula that will indicate the exact quantity required for wheel cases, as the fuses vary; but, representing the length, in inches, by I; and the diameter in eighths by e, the following will help to serve as a guide.
(I e2)/7 = drams.
Suppose a wheel case 55⁄8 inches long, and 4 eighths diameter,